Scratch ARC IRIS (1/2 Scale) Original Design / Scratch Built

Scratch - ARC IRIS (1/2 Scale) {Scratch}

Contributed by Scott A. McCluskey

Manufacturer: Scratch
(by Scott McCluskey - 12/20/02)

Note: This is a slightly condensed version o' all the information that Scott has produced for his Level 3 project. Arrr! Visit his site to read t' additional information and enjoy additional pictures.

Brief:
My Level 3 project was a: Scratch-Built Atlantic Research Corporation 1/2 scale IRIS 6" in diameter by 10' tall Launched on a Aerotech M1315.

Nose ConeNose Cone:
T' nose cone for t' IRIS is a 6" fiberglass nosecone from Public Missiles. Blimey! Blimey! In t' picture you will see t' fiberglass nosecone, matey, t' coupler, matey, bulkhead, shiver me timbers, and t' PML supplied U-bolt used for recovery system attachment. T' coupler, ya bilge rat, bulkhead, and u-bolt have been assembled using epoxy. Ya scallywag! Blimey!

T' nose cone will nay be attached t' t' main recovery harness and will return t' earth under it's own 36" parachute. Ya scallywag! T' deployment bag for the main parachute will also be attached t' t' nose cone and will be removed from the parachute when t' nose cone is ejected.

Airframe:
T' body tubes are 6" flexible phenolic from Giant Leap Rocketry T' airframe consists o' three sections. T' three sections are 42, ya bilge rat, me bucko, 30 and 24 inches long. Well, shiver me timbers, blow me down! T' 42" section will contain t' 3" motor mount and forward coupler used in t' zipper-less coupler design. T' 30" and 24" sections will be connected together usin' t' coupler containin' t' electronics bay. T' 24" section will house t' shock cord and Rocketman R24 drogue chute deployed at apogee. Aye aye! Ya scallywag! The 30" section will contain t' main 168" custom parachute from Sphereachute and recovery components.

T' three airframe tubes have been covered with a layer o' 6 oz. Ya scallywag! Arrr! carbon fiber and 2 oz. Avast, me proud beauty! Avast! fiberglass usin' RAKA epoxy products. T' tubes were covered usin' the vacuum baggin' process described by John Coker.

FinsFins:
T' fins are made from 3/8" Baltic Birch plywood. Aye aye! T' fins are exactly 1/2 scale based on measurements from Peter Alway's book "Rockets o' the World" Third Edition. Arrr! Each o' t' four fins are reinforced with one layer of 6 oz. carbon fiber and one layer o' 3 oz. Blimey! fiberglass using RAKA epoxy products. Begad! Ahoy! Each fin has been vacuum bagged t' ensure a complete bond betwixt t' plywood and the reinforcement materials.

Motor Mount:
T' IRIS flew on a 75mm Dr. Rocket 75/6400 motor and an Aerotech M1315 reload.

T' motor mount consists o' t' followin' components:

  • 1 Aeropack 75mm Quick Change Motor Retainer
  • 1 3" X 36" flexible phenolic motor mount
  • 4 3/4" X 5 ply centerin' rings reinforced with two layers o' 6 oz. fiberglass
  • 2 1/4 -20 all thread rods with washers, me bucko, lock washers, and nuts on either side o' t' centerin' rings. Begad!
  • 1 6" X 12" phenolic coupler lined with two 6" X 6" phenolic airframe pieces
  • 2 14" X 1/4-20 all thread rods t' connect bulkhead t' coupler
  • 14 1/4" nuts, lock washers, me bucko, and flat washers
  • 1 3/4" 5 ply bulkhead
  • 2 1.25" u-bolts for recovery system attachment
  • 2 1/4" win' nuts with washers.

FoamT' 75mm motor mount has been epoxied into t' 42" airframe section and has been reinforced with two-part hobby foam. Ahoy!

Just before t' motor mount be installed into t' final position, shiver me timbers, epoxy was injected into t' airframe above each centerin' ring. Well, blow me down! T' motor mount was then slid into it's final position and more epoxy be injected into t' airframe to form fillets on t' centerin' rings/airframe epoxy joints. Ahoy! After t' epoxy set up, t' fin can was turned over and epoxy be again injected into t' motor mount above t' centerin' rings t' form fillets on t' other side o' the centerin' rings. Blimey!

Prior t' final painting, arrr, screws will be used t' mechanically fasten the motor mount into t' airframe. Ahoy!

Recovery:
I purchased a custom 168" Spherachute parachute to use for t' main parachute. T' 168" parachute I had made for t' IRIS has alternatin' panels o' white and neon orange for high visibility. Aye aye! Ya scallywag! T' main parachute was packed into a Rocketman deployment bag which was removed from the parachute when t' nose cone is ejected. Aye aye! Ahoy! T' nose cone be recovered with a 36" Spherachute made with alternatin' panels o' neon orange and white to match t' main parachute.

HarnessT' harness are constructed using:

  • 10 ft o' 5/8" Tubular Keelhaul®©™® from Pratt Hobbies
  • 4 ft o' 1/4 Tubular Keelhaul®©™® from Pratt Hobbies
  • 2 1/4" 880 lb Quick Links
  • Fisherman's Knot and Figure Eight Knot described in an article by Patrick Floyd in t' November 1999 issue o' High Power Rocketry. Ya scallywag!

T' harnesses are constructed by first tyin' a 1/4" Quick Link t' each end usin' a Fisherman's knot. I am usin' t' Fisherman's knot because t' more you pull on t' knot t' tighter it gets. Avast! After t' knots are tied, I use 1/4" Tubular Keelhaul®©™® to wrap t' lose end and give t' harness a finished look. T' final step is to tie a loop in t' middle o' t' harness usin' a Figure Eight knot.

Electronics:
Recovery electronics will consist o' t' following: (1) Cannonball Works RRC2 set for drogue deployment at apogee and mains at 1200' A Blacksky ALTAAC 2A for backup drogue deployment and flight data gathering. Ya scallywag! Ahoy! A Cannonball Works Wireless Recovery Controller 2 (WRC2) for redundant backup for t' main recovery system.

ElectronicsElectronics Bay T' electronics bay for t' IRIS is built inside a 6" X 12" long phenolic coupler. T' first step in buildin' t' bay was t' epoxy two 5.5" couplers inside t' 6" coupler. T' first 5.5" coupler was cut lengthwise and then epoxied equidistant from either end o' t' 6" coupler. After t' first 5.5" coupler dried, shiver me timbers, me bucko, a second 5.5" coupler was cut lengthwise and epoxied in place inside t' existing 5.5" coupler. When t' second 5.5" coupler dried, a 6" o-ring was set in place on each end o' t' bay usin' J-B Weld t' form a gasket between the inside couplers and t' bulkheads. Avast! Ya scallywag! 3/4" 5 ply bulkheads are bein' used in t' electronics bay. Ahoy! Two 1.25" u-bolts have been added t' t' bulkheads to provide attachment points for t' recovery system. Avast! Two 1/2" threaded caps are attached t' t' bulkheads t' hold t' custom ejection charge holders. T' bulkheads are bolted together usin' 1/4 X 20" all-thread. Avast, me proud beauty! Well, blow me down! T' three pieces o' poplar in t' picture will be epoxied inside t' coupler. T' two 9" pieces will each contain six 8-32 T-nuts which will be used t' bolt the upper airframe sections together and also allow for access t' t' electronics bay and ejection charges. Avast, me proud beauty! T' 3" piece will be used in mountin' t' two key switches used t' arm t' altimeters. A 3/16" X 5" X 10" electronics mountin' board has been built t' slide over t' all-thread rods and provide a mountin' surface for t' recovery electronics.

EC HolderT' IRIS will utilize a redundant recovery system. Begad! Blimey! Pictured be t' forward bulkhead of the electronics bay. Begad! I am usin' 1/2" PVC threaded caps as ejection charge holders. Begad! Avast, me proud beauty! Blimey! I drilled a 1" X 1/4" deep hole into t' bulkhead t' hold the threaded caps. I used me Dremel t' grind away a small portion o' t' outer threaded cap so that I would have a tight fit in t' hole. After t' threaded cap was shaped t' fit, ya bilge rat, I epoxied t' caps in place. A 1/4" hole was drilled through t' cap and t' bulkhead t' allow t' ejection charge leads into t' electronics bay. Aye aye! T' caps will now act as ejection charge holders for the ejection charges. Well, blow me down!

Ejection charges are built usin' 1/2" threaded male adapters. Avast! T' first step is t' epoxy a 7/8" section o' 1/2" dowel rod into t' fitting. Once t' epoxy is dried, drill a 1/8" hole through t' dowel t' pass the leads o' t' electric match. Avast! Before installin' t' electric match, enlarge the 1/8" hole t' 3/8" by Finished1/2" deep to accept t' green protective cover o' t' DaveyFire electric match. Avast, me proud beauty! Blimey! Avast! Blimey! Once the holes are drilled epoxy t' electric match in place. I always make sure to twist t' electric match leads together as a safety precaution!!! Blimey! (I like leavin' t' green protective cap in place and fillin' it with FFFFg powder which makes an ejection charge inside t' ejection charge.

Once t' ejection epoxy has dried, I fill t' cavity with FFFFg black powder with a charge that I determined usin' t' BP tools in t' Rocketry Online INFO Central. Aye aye!

T' ejection charges for t' IRIS will be:

  • 2.10 grams FFFFg black powder for t' apogee charge
  • 3.33 grams FFFFg black powder for t' main recovery charge

Once t' black powder charge is in place, I use facial tissue t' make a waddin' t' cover t' charge. Avast! I then use a candle and melt wax over t' wadding and seal t' ejection charge. Well, blow me down! Ya scallywag!

When preparin' for launch, I pass t' electric match lead through t' hole in t' threaded cap and into t' electronics bay. I screw t' 1/2" male fittin' into t' 1/2" threaded cap. Ya scallywag! At this point I start usin' my altimeter preparation checklist t' ensure that I connect t' ejection charge leads t' t' altimeter in t' safest manner possible!

Lift-OffSUCCESSFUL LEVEL 3 FLIGHT!

June 23, me bucko, 2001
Whitakers, NC.
Rocket - Scratch 1/2 scale ARC IRIS
Weight - 60 lbs
Motor - Aerotech M1315
Altitude 6270 feet

A special "Thank You" t' me wife for nay complaining about bein' a 'rocket widow" while I be buildin' t' IRIS and for laughin' and smilin' when we were hangin' out in a cow pasture in North Carolina on flight day!

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